Cytochrome P450 and Glutathione S-Transferase Confer Metabolic Resistance to SYP-14288 and Multi-Drug Resistance in Rhizoctonia solani

Fluazinam Resistance in Colletotrichum gloeosporioides and Its Association with Metabolic Detoxification and Efflux

Colletotrichum gloeosporioides is a major pathogen causing anthracnose of pepper (Capsicum annuum). In agricultural production, it is typically managed using fungicides like fluazinam. However, the frequent use of fungicides raises concerns about the potential development of fungicide resistance. This issue has not been extensively documented. To address this, 102 isolates of C. gloeosporioides were collected from pepper in fields. The EC50 values of these isolates to fluazinam exhibited a unimodal distribution with a mean value of 0.18 ± 0.14 μg/mL, indicating the absence of naturally occurring resistance in the sampling region. Through fluazinam domestication, 35 fluazinam-resistant mutants were obtained from the parental strain Cg219. These mutants exhibited strong cross-resistance to the fungicide SYP-14288. Metabolic analysis revealed that C. gloeosporioides could metabolize fluazinam into compounds lacking antifungal activity. Genetic analysis showed that genes related to efflux and detoxification were upregulated to varying degrees in both fluazinam-resistant mutants and fluazinam-treated strains. By comparing fungal growth and pathogenicity between the mutants and their parent, the mutants showed impaired overall fitness. Therefore, C. gloeosporioides has a low risk of developing resistance to fluazinam. This study provides critical data for monitoring the emergence of fungicide resistance and developing resistance management strategies for fluazinam.

Understanding Efflux-Mediated Multidrug Resistance in Botrytis cinerea for Improved Management of Fungicide Resistance

Botrytis cinerea is a major fungal pathogen infecting over 1400 plant species. It poses a significant threat to agriculture due to multiple fungicide resistance and multidrug resistance, involves resistance to fungicides with different modes of action. Multiple fungicide resistance is mostly due to an accumulation of point mutations in target genes over time, and MDR is result from efflux (e-MDR) and metabolism (m-MDR). This review introduces the occurrence of e-MDR of B. cinerea, the key mechanisms, origins and management strategies of e-MDR in fields. New materials such as nanomaterials become a strategy to overcoming MDR via inhibition of ABC transporter. A deeper understanding of efflux-mediated MDR will provide a support for the MDR management of B. cinerea and the efficient utilization of fungicides.

Exploring the Molecular Mechanisms of Resistance to Prochloraz by Lasiodiplodia theobromae Isolated from Mango

Mango stem-end rot caused by Lasiodiplodia theobromae is a major postharvest disease in China. Prochloraz is commonly used for disease control in mango orchards and in storage. However, prochloraz resistance has been detected in L. theobromae. This study aimed to explore the underlying mechanisms responsible for prochloraz resistance in L. theobromae. The results show that no point mutation in the target gene LtCYP51 of the prochloraz-resistant L. theobromae strain was detected, but the expression was upregulated significantly. Additionally, the full-length sequences of the cytochrome P450 gene CYP55A3 were successfully amplified and identified from L. theobromae, and the qRT-PCR results confirm that CYP55A3 was significantly upregulated after treatment with prochloraz. The knockout mutant of the CYP55A3 presented significantly lower gene expression levels than the wild-type strain HL02, with a 16.67-fold reduction, but a 1.34-fold reduction in P450 activities and a 1.72-fold increase in the accumulation of prochloraz in the mycelia. Treatment with the P450 enzyme inhibitor significantly synergized with the prochloraz toxicity. The wild-type strain was highly resistant to pyraclostrobin and carbendazim; similarly, the sensitivity of the knockout mutant to pyraclostrobin and carbendazim also notably increased. There was no significant difference between the wild-type strain and the gene-complemented strain. The homology model and molecular docking analysis provide evidence that prochloraz interacts with the protein structure of CYP55A3. These findings suggest that the overexpression of the target gene LtCYP51 and the detoxification gene CYP55A3 were involved in the molecular mechanisms of resistance to prochloraz by L. theobromae.

Carboxylesterase and Cytochrome P450 Confer Metabolic Resistance Simultaneously to Azoxystrobin and Some Other Fungicides in Botrytis cinerea

Plant pathogens have frequently shown multidrug resistance (MDR) in the field, often linked to efflux and sometimes metabolism of fungicides. To investigate the potential role of metabolic resistance in B. cinerea strains showing MDR, the azoxystrobin-sensitive strain B05.10 and -resistant strain Bc242 were treated with azoxystrobin. The degradation half-life of azoxystrobin in Bc242 (9.63 days) was shorter than that in B05.10 (28.88 days). Azoxystrobin acid, identified as a metabolite, exhibited significantly lower inhibition rates on colony and conidia (9.34 and 11.98%, respectively) than azoxystrobin. Bc242 exhibited higher expression levels of 34 cytochrome P450s (P450s) and 11 carboxylesterase genes (CarEs) compared to B05.10 according to RNA-seq analysis. The expression of P450 genes Bcin_02g01260 and Bcin_12g06380, along with the CarEs Bcin_12g06360 in Saccharomyces cerevisiae, resulted in reduced sensitivity to various fungicides, including azoxystrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin, iprodione, and carbendazim. Thus, the mechanism of B. cinerea MDR is linked to metabolism mediated by the CarE and P450 genes.

N6-methyloxyadenine-mediated detoxification and ferroptosis confer a trade-off between multi-fungicide resistance and fitness

Multi-fungicide resistance (MFR) is a serious environmental problem, which results in the excessive use of fungicides. Fitness penalty, as a common phenomenon in MFR, can partially counteract the issue of resistance due to the weakened vigor of MFR pathogens. Their underlying mechanism and relationship remain unexplained. By Oxford Nanopore Technologies sequencing and dot blot, we found that N6-methyloxyadenine (6mA) modification, the dominate epigenetic marker in Phytophthora capsici, was significantly altered after MFR emerged. Among the differently methylated genes, PcGSTZ1 could efficiently detoxify SYP-14288, a novel uncoupler, through complexing the fungicide with glutathione and induce MFR. Interestingly, PcGSTZ1 overexpression was induced by elevated 6mA levels and chromatin accessibility to its genomic loci. Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in P. capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. In conclusion, the findings provide new insights into the biological role of 6mA as well as the mechanisms underlying the trade-off between MFR and fitness. These could also benefit disease control through the blockade of the epigenetic axis to resensitize resistant isolates.IMPORTANCEN6-methyloxyadenine (6mA) modification on DNA is correlated with tolerance under different stress in prokaryotes. However, the role of 6mA in eukaryotes remains poorly understood. Our current study reveals that DNA adenine methyltransferase 1 (DAMT1)-mediated 6mA modification at the upstream region of GST zeta 1 (GSTZ1) is elevated in the resistant strain. This elevation promotes the detoxification uncoupler and induces multifungicide resistance (MFR). Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in Phytophthora capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. Overall, our findings uncover an innovative mechanism underlying 6mA modification in regulating PcGSTZ1 transcription and the ferroptosis pathway in P. capsici.

Multidrug resistance of Botrytis cinerea associated with its adaptation to plant secondary metabolites

Fungicides are an effective way to control gray mold of grapes, but the pathogen Botrytis cinerea can develop resistance, overcoming the effectiveness of a fungicide that is repeatedly applied. More importantly, the emergence of multidrug resistance (MDR) in the field, where multiple fungicides with different modes of action simultaneously lose their efficacies, is a significant concern. MDR is associated with ATP-binding cassette (ABC) transporters of the pathogen, and certain plant secondary metabolites (PSMs) stimulate the upregulation of ABC transporters, we hypothesized that the pathogen's preadaptation to PSMs might contribute to MDR development. To test this in B. cinerea, ten PSMs, namely, resveratrol, reserpine, chalcone, flavanone, eugenol, farnesol, anethene, camptothecin, salicylic acid, and psoralen, were selected based on their association with ABC transporters involved in fungicide resistance. B. cinerea strain B05.10 was continuously transferred for 15 generations on potato dextrose agar amended with a PSM (PDAP), and sensitivities to PSMs and fungicides were examined on the 5th, 10th, and 15th generations. RNA was extracted from B. cinerea from the selected generations. After 15 generations of culture transfers, an up-regulation was observed in the expression of ABC transporter-encoding genes BcatrB, BcatrD, and BcatrK using quantitative polymerase chain reaction (qPCR). This upregulation was found to contribute to MDR of B. cinerea against two or more fungicides, among azoxystrobin, boscalid, fludioxonil, difenoconazole, prochloraz, and pyrimethanil. This finding was confirmed through genetic transformation. The decreased sensitivity of B. cinerea to fungicides was confirmed as a subsequent MDR phenotype after exposure to camptothecin, flavanone, and resveratrol. Besides, transcriptome analysis also revealed the upregulation of transcription factors related to ABC expression following resveratrol exposure. This suggests that PSMs contributed to inducing preadaptation of B. cinerea, leading to subsequent MDR.IMPORTANCEThe emergence of MDR in plant pathogens is a threat to plant disease management and leads to the use of excessive fungicides. Botrytis cinerea is of particular concern because its MDR has widely emerged in the field. Understanding its genesis is the first step for controlling MDR. In this study, the contribution of PSMs to MDR has been examined. Effective management of this pathogen in agroecosystems relies on a better understanding of how it copes with phytochemicals or fungicides.

ABC transporters linked to multiple herbicide resistance in blackgrass (Alopecurus myosuroides)

Enhanced detoxification is a prominent mechanism protecting plants from toxic xenobiotics and endows resistance to diverse herbicide chemistries in grass weeds such as blackgrass (Alopecurus myosuroides). The roles of enzyme families which impart enhanced metabolic resistance (EMR) to herbicides through hydroxylation (phase 1 metabolism) and/or conjugation with glutathione or sugars (phase 2) have been well established. However, the functional importance of herbicide metabolite compartmentalisation into the vacuole as promoted by active transport (phase 3), has received little attention as an EMR mechanism. ATP-binding cassette (ABC) transporters are known to be important in drug detoxification in fungi and mammals. In this study, we identified three distinct C-class ABCCs transporters namely AmABCC1, AmABCC2 and AmABCC3 in populations of blackgrass exhibiting EMR and resistance to multiple herbicides. Uptake studies with monochlorobimane in root cells, showed that the EMR blackgrass had an enhanced capacity to compartmentalize fluorescent glutathione-bimane conjugated metabolites in an energy-dependent manner. Subcellular localisation analysis using transient expression of GFP-tagged AmABCC2 assays in Nicotiana demonstrated that the transporter was a membrane bound protein associated with the tonoplast. At the transcript level, as compared with herbicide sensitive plants, AmABCC1 and AmABCC2 were positively correlated with EMR in herbicide resistant blackgrass being co-expressed with AmGSTU2a, a glutathione transferase (GST) involved in herbicide detoxification linked to resistance. As the glutathione conjugates generated by GSTs are classic ligands for ABC proteins, this co-expression suggested AmGSTU2a and the two ABCC transporters delivered the coupled rapid phase 2/3 detoxification observed in EMR. A role for the transporters in resistance was further confirmed in transgenic yeast by demonstrating that the expression of either AmABCC1 or AmABCC2, promoted enhanced tolerance to the sulfonylurea herbicide, mesosulfuron-methyl. Our results link the expression of ABCC transporters to enhanced metabolic resistance in blackgrass through their ability to transport herbicides, and their metabolites, into the vacuole.